This program project serves as the nucleus of the NIH supported programs in the Gerontology Center of Boston University. The objective is to learn why animals age, both in terms of general biochemistry of aging but specifically in two tissue systems, the brain and connective tissue. The brain is a complex organ so that within the brain we study the auditory cortex and olfactory bulb and since the anatomy of the auditory cortex cannot be separated from its function we study the auditory system as a whole with both anatomical, biochemical and behavioral techniques. The biochemical studies emphasize the structure of chromatin and what happens during aging, both to DNA in terms of somatic mutation and to the proteins which control the expression phenotype. The connective tissue studies have emphasized the internal cross linkage of elastin and collagen as well as their interaction with the glycoproteins of connective tissue. Our interdisciplinary studies use techniques as diverse as electron microscopy, studies of circular dichroism and operant conditioning. We hope to learn essential information about the aging brain and the relationship of biochemical, morphological and behavioral change during age. It is felt that only through the cooperation of investigators from a broad range of disciplines can coherent evaluation of the causes of aging contribute to a fruitful understanding and its effect on man be obtained.